502 G. H. PARKER 



rachis and flows out with equal freedom from the mouths of the 

 autozooids over the whole superior surface. If a similar injec- 

 tion is made into the smaller cavity, the colored fluid flows out of 

 only one orifice. This is near the middle of the superior face of 

 the rachis, and at the end of an axial band of somewhat smooth 

 tissue that leads from near the root of the peduncle over the 

 rachis to the region of its center. This orifice was first identi- 

 fied by Miiller ('64, p. 354), who described it as the general inlet 

 for the whole canal system of Renilla. Kolliker (72) suspected 

 it to be the mouth of the axial zooid, but Wilson's studies ('84) 

 on the embryology of Renilla showed it to be a much enlarged 



Fig. 1 Diagram of a median section of the rachis (R) and the peduncle (P) 

 of Renilla, showing the orifice (0) into the superior canal (S), which, near the 

 distal end of the peduncle, connects through the transverse septum with the 

 inferior canal (I). This in turn communicates with the bases of the zooids (Z), 

 whose mouths are open to the exterior. 



siphonozooid. It was believed by Wilson ('84, p. 725) to be an 

 exhalent orifice, the other siphonozooids serving as means of» 

 entrance for the water. If the connection of this orifice with the 

 smaller cavity in the peduncle is dissected out, it is found to be 

 a well-defined tube, extending from the external opening over 

 the superior face of the rachis, where its course is marked by the 

 band of smooth tissue already referred to, to the peduncle, 

 down whose whole length it can be followed as the superior canal 

 of that structure. The inferior canal in Renilla can also be shown 

 to extend from the end of the peduncle through the length of that 

 structure and into the inferior portion of the rachis, where it 



